Production of gas-releasing electrolyte-replenishing Ah-scale zinc metal pouch cells with aqueous gel electrolyte

Aqueous zinc batteries are ideal candidates for grid-scale energy storage because of their safety and low-cost aspects. However, the production of large-format aqueous Zn batteries is hindered by electrolyte consumption, hydrogen gas evolution and accumulation, and Zn dendrites growth. To circumvent these issues, here we propose an “open” pouch cell design for large-format production of aqueous Zn batteries, which can release hydrogen gas and allow the refilling of the electrolyte components consumed during cell cycling. The cell uses a gel electrolyte containing crosslinked kappa (k)-carrageenan and chitosan. It bonds water molecules and hinders their side reaction with Zn, preventing electrolyte leakage and fast evaporation. As a proof-of-concept, we report the assembly and testing of a Zn | |ZnxV2O5·nH2O multi-layer “open” pouch cell using the carrageenan/chitosan gel electrolyte, which delivers an initial discharge capacity of 0.9 Ah and 84% capacity retention after 200 cycles at 200 mA g‒1, 370 kPa and 25 °C.

cell using GF. Is this due to the low ionic conductivity of CarraChi gel-ZnSO4? Also, the authors claimed that using CarraChi gel-ZnSO4 can increase the CE of Zn/Cu cells. Due to some error points that show abnormal CEs for CarraChi gel-ZnSO4 cell, the average CE of cell using CarraChi gel-ZnSO4 might be similar or a little higher than the cell of GF, but it seems like Zn/Cu cell using GF has higher CEs in most of the cycles before the 150th cycle. Please provide reasonable explanations for these circumstances.
8. Please provide the current density condition used for comparing the SEM image in Fig. 3f, and Supplementary Fig. 9a, b). 9. Why is the rate capability of the full cell using CarraChi gel-ZnSO4 better than the reference case? I believe using CarraChi gel-ZnSO4 can impinge the overpotential as is proved in Zn/Zn cell test. Please also provide the voltage profile of the Zn|GF|ZVO and compare it in Fig. 5a.
10. Lastly, please compare the refillable pouch cell test result in Fig. 4g and Fig. 5f with the GF cells.
Reviewer #3 (Remarks to the Author): The present manuscript proposed a hydrogel that can be prepared on a large scale and a refillable battery design. Indeed, the overall electrochemical performance of the ZIBs has been improved in this study. However, the work fails to reflect the big progress in the development of high-performance ZIBs. Many studies proposed hydrogel systems. The current work just selected a different raw material that has been commercialized. The proposed battery design also disables addressing the key challenge of ZIBs, such as HER and long-cycling stability of the cathode. In all, the proposed concept of the scalable synthesis of hydrogel and battery design can not present an impressive innovation. Thus, I do not support the acceptance of the manuscript for publication in the present form.
More issues are listed as follows: 1. The authors proposed a hydrogel enabling to suppress the electrolyte loss. However, why do the authors need to refill the water? Refilling water means that the electrolyte will be consumed or can not be preserved very well in this system. In this situation, there is an obvious contradiction between the proposed concept and experimental results. Meanwhile, the authors should clarify why the electrolyte is consumed or can not be preserved even though hydrogel has been used in this manuscript. Does the refilled water affect the electrolyte concentration and further the electrochemical performance? If it does, it represents that the as-proposed battery design may fail to maintain the electrochemical performance. If it doesn't, the authors need to elaborately explain why the electrochemical performance does not change even though the electrolyte concentration changes after refilling the water. Additionally, as claimed that the hydrogel can suppress HER, but why do the authors still need to design a gas outlet? 2. K-carrageenan and chitosan have been successfully commercialized for many years. Therefore, largescale preparation of hydrogel using these two raw materials is not an innovation of this manuscript.
3. Figure 2h demonstrated that the tensile stress of Carrachi-ZnSO4 has evidently decreased compared with CarraChi, suggesting that some chemical bonds have changed in this gel because of Zn2+. Please make a detailed explanation of what happened to the gel when Zn2+ was added. Authors should also supplement the visualization proof to demonstrate the gel can prevent dendrite penetration.
4. Which type of GF is used in this work? The authors should mention the details of GF in the experimental section. This is very important for those who want to repeat this experiment. In addition, the thickness of GF should be at around 50 µm at least. Unfortunately, the thickness of CarraChi gel and GF is different when the authors compare the electrochemical performance, which may affect the conclusions. Please compare the electrochemical performance with the same thickness of CarraChi and GF.
5. Could the author describe what kind of barrier the gel layer provides for Zn surface diffusion?
6. It will be nice if the author could perform some simulations to visualize the electric field at the electrolyte-electrode interface that has been homogenized when gel electrolyte is used in this study.
7. "1.26V vs RHE at 5 mA cm-2 (S Fig. 12)" Please change Fig. 12 to Fig. 10. In Fig. 10, it indeed verifies HER can not be fully suppressed even using CarraChi gel because the onset potential for HER is almost the same, in which both start around -1.1V. The difference is that the gel system shows a smaller current density compared with GF. In this case, it is incorrect to claim Fig. 10 demonstrates slower evolution kinetics. Importantly, please use ZnSO4 electrolyte rather than NaSO4 electrolyte to test LSV.
8. The calculation of average CE in the symmetric system in this manuscript is wrong. Please refer to Nat Energy 5, 743-749 (2020). https://doi.org/10.1038/s41560-020-0674-x for your average CE calculation. 9. It should be more subjective when the authors conclude. The good capacity retention of Zn|CarraChi|ZVO is not only related to the effective suppression of Zn dendrite growth but also the inhibition of self-corrosion and side reactions of Zn foil.
10. The author should explain why ZVO in GF almost shows the same specific capacity as CarraChia before 40 cycles in Figure 5c, while the specific capacity of GF is higher or lower than CarraChi in Figure  5b. Please mention which current density has been used in Figure 5f.
2 It is true that many gel electrolytes have been developed for ZIBs. The shortcomings and research gaps are the small overall capacity of the batteries, which may hinder their application in ZIBs as energystorage devices. In this work, we mainly focus on large-scale energy storage of the aqueous ZIBs.
The reviewer's comments motivated us to add more background information on polymer gel electrolytes in ZIBs in general. We further compare the advantages and disadvantages of the CarraChi with previously reported hydrogel electrolytes in Table R1 and add related references in the Revised Manuscript. It is seen that our work with the new battery design and the CarraChi gel electrolyte presents a much improved overall capacity for use as large-scale energy-storage batteries. We conducted EIS before and after cycling for 4000 h. It is seen that the Rct decreases to some extent after cycling, which is ascribed to the improved reaction kinetics during cycling (Fig. R1). This further certifies the normal operation of the pouch symmetric cell.

Fig. R1
. EIS curves of the Zn|CarraChi|Zn symmetric cell before and after cycling for 4000 h.

Updates in the Revised Manuscript:
We have added the EIS curves of Zn|CarraChi|Zn symmetric cells before and after cycling in the Revised Manuscript (Fig. 4g). We have also added the following discussion in the Revised Manuscript: Line 217-219, Page 13: "The electrochemical impedance spectroscopy (EIS) curves before and after cycling also confirm that no short circuit occurred during cycling (Fig. 4h)." Line 345-347, Page 20: "The water refilling procedure was conducted when the overpotential increased obviously in comparison to the initial overpotential, and 0.5 ml g -1 (ratio of electrolyte to the active ZVO) electrolyte was injected every time. The battery is subjected to a pressure of 370 kPa during the testing process."

5.
It is unclear how tiny hydrogen bubbles leave the zinc surface, mainly when the viscous gel electrolyte covers the surface. Can some of these tiny hydrogen bubbles possibly accumulate on the surface and isolate the zinc surface from the electrolytes? 6 Reply: We thank the reviewer for this interesting question. To observe how the hydrogen bubbles form and accumulate on the interface between the Zn and gel electrolyte during the plating process, we carried out in situ optical microscope observation during Zn deposition (10 mA cm -2 ). However, during the Zn deposition process, we did not find obvious bubbles accumulating on the Zn surface or isolating Zn from the gel electrolyte (Fig. R2).
If there were any accumulation of H2 bubbles or Zn separation from the gel electrolyte, we should have found non-uniform Zn deposition or increased interface resistance after cell cycling. On the contrary, SEM images show uniform Zn morphology (Fig. 4h), and the Rct after cycling is reduced (Fig. R1), indicating that there were no H2 bubbles accumulating on the surface or isolating the Zn surface from the electrolyte. We speculate that any generated H2 would diffuse and escape from the open cells before accumulation.

Fig. R2.
In situ optical microscope images of Zn foil during plating at 10 mA cm −2 , without finding H2 bubbles.

Updates in the Revised Manuscript:
We have added the in situ optical microscope images of Zn foil during plating in Supplementary Fig.   11 R3a). SEM images also reveal that a smooth surface of the Zn foil can be observed with CarraChi (Fig.   R3b). In contrast, the Zn foil soaked in 2M ZnSO4 solutions is covered with dendritic by-products of zinc hydroxide sulfate (Fig. R3c). Therefore, the CarraChi gel has a positive effect on mitigating the zinc hydroxide sulfate byproducts.

Updates in the Revised Manuscript:
We have added the XRD patterns and SEM images of Zn foil soaked with CarraChi gel electrolyte and ZnSO4 in the revised Supplementary Information (Supplementary Fig. 12). We have also added the following discussion in the Revised Manuscript to elaborate on the effect of CarraChi on the interface stability: 8 Line 156-160, Page 9: "The CarraChi gel electrolyte also reduces corrosion reactions between the Zn foil and ZnSO4, which is proved by the weaker peak intensity of by-products in the X-ray diffraction (XRD) patterns and the smooth surface in the SEM images in the anti-corrosion experiment compared to the Zn anode with liquid electrolyte and GF separator ( Supplementary Fig. 12)."

7.
The capacity of the cell is measured to the cut-off voltage approaching 0 V, which is not practical for real applications. Anyway, the authors should compare their results with other results reported for liquid electrolytes of vanadium-oxide-based cells.

Reply:
We thank the reviewer for the helpful suggestion. V2O5-based cathodes have been widely studied in the literature due to their high specific capacity. We find it is a common practice to apply the voltage range of 0.2-1.6 V for the V2O5-based cathode (Nat. Energy 2016, 1, 16119; ACS Appl. Mater. Interfaces, 2021,13, 30594-30602).
According to the reviewer's comment, we compared the electrochemical performance of our refillable Zn batteries with previously reported vanadium-oxide-based cells in the literature (using liquid electrolytes) in Table R2. Our pouch cell with the CarraChi gel electrolyte has a maximum capacity of 0.9 Ah and excellent cycling stability, retaining 84% capacity after 200 cycles, which is much better than the previously reported pouch full cells.

Updates in the Revised Manuscript:
We have added the performance comparison table (Table R2)  has an initial capacity of 0.9 Ah and excellent cycling stability, retaining 84% capacity after 200 cycles, superior to full cells using liquid electrolytes and GF separator ( Fig. 5f and Supplementary Fig. 22).
This performance is also much better than that of the previously reported pouch full cells

Reply:
We thank the reviewer for the reviewer's helpful suggestion. We have carefully read these recommended papers and compared the advantages and disadvantages of these polymer gels with our work. We have summarized the characteristic performances of gel electrolytes for Zn batteries (including the reviewer-suggested ones) and ours in Table R1 (page 2 of the Response Letter) for comparison.
It is found that gel electrolytes present high Zn 2+ transference numbers and good ionic conductivity (Table R1), which are the advantages of gel electrolytes and exactly the reason why we chose a gel electrolyte to demonstrate our refillable battery configuration. The disadvantage of the previously reported gel electrolytes mainly lies in the relatively low current density and capacity, which may not meet the requirements of practical Zn batteries. In contrast, we focus on practical Zn batteries with a refillable and large-format configuration, taking advantage of the gel electrolyte and enabling operation under high current densities and large capacities.

Updates in the Revised Manuscript:
We have added the It was quite clever that the authors made a hole in the pouch cell to refill the water and to let the gaseous side-reaction products easily be removed away. I also personally believe that there is no reason for aqueous batteries to follow the conventional closed-type configurations of alkali metal-based batteries considering that the aqueous batteries can retain air or humid conditions. So, I do think proposing a new configuration, although there was a small change, can encourage researchers in the relevant field to think more broadly about cell design. However, I see there are lots of ambiguous speculations which require precise explanations, and more detailed comparisons with the reference Zn batteries are necessary. In light of all these circumstances, a rigorous major revision of this paper is recommended.
The comments are shown below. Without precise explanations of every comment, this paper should be published in other journals.

Reply:
We thank the reviewer for recognizing the novelty of our work and providing professional suggestions. We particularly agree with the reviewer that "there is no reason for aqueous batteries to follow the conventional closed-type configurations of alkali metal-based batteries" and "a new configuration, although there was a small change, can encourage researchers in the relevant field to think more broadly about cell design". We have modified the Introduction and Conclusions based on the reviewer's comments to better highlight the importance of the new cell design.
According to the reviewer's comments, we have conducted more experiments and added more discussion and detailed comparisons to demonstrate the hypothesis clearly. All the concerns have been considered seriously and addressed in the Revised Manuscript. Please see below our point-by-point responses. 12 1. First of all, why would the formation of hydrogen bonds between the water molecules and CarraChi gel-ZnSO4 reduce the HER? I know it is a conventional argument typically used in aqueous battery systems, but I don't see the scientific background of this argument. Also, the part saying that "the decrease of the non H-bond contents indicates a weaker water activity" should be clearly explained.
Perhaps, the authors' perspectives on changes in electronic structure, and experimental results on changes in solvation structure might be meaningful.

Reply:
We thank the reviewer for the insightful comments.
It is true that the relation between hydrogen bonding (H-bonding), water activity, and the HER has not been well understood. We wish to explain based on the literature and our experimental results.
According to Grotthuss mechanism of proton transport, proton transfers by means of concerted the hydrogel electrolyte and free water molecules destructs the H-bond network between water molecules, impedes the transport of protons, and thus reduces the water activity and HER.
In our work, we found that the CarraChi gel electrolyte forms H bonds with the water molecules and breaks the H-bond network of water molecules, as evidenced by Raman spectra (Supplementary Fig.   9). We also demonstrated that the HER in the CarraChi gel electrolyte is effectively suppressed compared with the Zn anodes in the aqueous electrolyte by LSV and in situ optical microscope (Supplementary Fig. 10 and 11). Thus, the formation of H bonds between the water molecules and CarraChi gel electrolyte suppresses the HER, in good agreement with the above mechanism discussed in the literature. 13 In addition, we agree with the reviewer's comments that the solvation structure has a direct impact on desolvation and HER mitigation. To reveal the changes in the solvation structure of Zn 2+ , we further measured the Zn nuclear magnetic resonance ( 67 Zn NMR) for the ZnSO4 solution and CarraChi gel electrolyte (Fig. R4). The 67 Zn chemical shift of the CarraChi gel electrolyte is slightly higher than that of the ZnSO4 electrolyte, indicating that the CarraChi gel molecules replace bound H2O molecules in the optimized Zn 2+ solvation sheath, which is in agreement with the Raman results. The changed solvation structure is considered a factor in decreasing the water activity and mitigating the HER.

Updates in the Revised Manuscript:
We have added the following discussion in the Revised Manuscript: The authors showed LSV data to claim that CarraChi gel-ZnSO4 can suppress the HER. However, it is questionable why the authors obtained the overpotential at 5 mA cm -2 . Normally, we are interested in the on-set potential of HER. If the authors want to claim the kinetically suppressing effect of CarraChi gel-ZnSO4 on HER in the way they used in the paper, it is necessary to show that the overpotential of the Zn redox reaction is lower than the reference case. Otherwise, the method the authors used will show the effects of low ionic conductivity (5.3 mS cm -1 , which is lower than the typically reported ionic conductivity of aqueous 2M ZnSO4 electrolyte), which will obviously show a higher overpotential for both the Zn redox reaction and HER. By the way, you should change

Reply:
We thank the reviewer for the constructive suggestion. We fully agree with the reviewer's comment that the onset potential of HER is important to evaluate the HER kinetics and the ionic conductivity will affect the overpotential of HER. Thus, instead of comparing the overpotential at 5 mA cm −2 , we compared the onset potential of HER in symmetric cells. To eliminate the effect of ohm resistance on the measurement results, we carried out iR correction for the LSV curves and calculated the onset potential for HER (

Updates in the Revised Manuscript:
We have updated the LSV curves and onset potentials in the revised Supplementary Information ( Supplementary Fig. 10). We also corrected the figure index errors from Fig. 10 to Fig. 11. We have also added the following discussion in the Revised Manuscript: Line 152-154, Page 9: "The suppressed HER on the Zn anode with CarraChi is also proved by a much lower onset overpotential (−1.40 V vs. standard hydrogen electrode, SHE) than that with a GF separator (−1.26 V vs. SHE) ( Supplementary Fig. 10)."

3.
Where did the C-N-C bond come from in Supplementary Fig. 3b? Also, I believe Fig. 2g needs to be revised. In the manuscript, it is said that Fig. 2g is about the FT-IR result comparing the spectrum of k-carrageenan and chitosan with CarraChi. However, there are only spectra of CarraChi and CarraChi gel-ZnSO4 in Fig. 2g. As a result, I could not clearly observe the red shift of the -OH/-NH2 peak in CarraChi.

Reply:
We thank the reviewer for the helpful comments. Following the reviewer's comments, we double-checked the peak information of N species in Supplementary Fig. 3 and corrected the bond information. The peak located at 399.5 eV is ascribed to the C-N bond (Fig. R6b). 16 We revised Fig. 2g and added the FTIR curves of CarraChi gel, chitosan, and k-carrageenan in the updated figure. In comparison to the chitosan and k-carrageenan, a clear red shift of the -OH/-NH2 peak can be observed from 3256.7 to 3136.3 cm -1 in CarraChi (Fig. R7).

Updates in the Revised Manuscript:
We have corrected the bond information of the N1s in Supplementary Fig. 3 in the revised Supplementary Information. We have also revised the FTIR curves in Fig. 2g

Updates in the Revised Manuscript:
We have further updated the chronoamperometry and EIS curves in Supplementary Fig. 6 Table 3)."

6.
Please provide the zeta potential of GF in a neutral solution before and after the addition of ZnSO4.

Reply:
We thank the reviewer for the helpful suggestion. Following the comment, we tested the zeta potential of pulverized GF in a neutral solution before and after the addition of ZnSO4. The zeta potential of GF powder is −26.4 mV (Fig. R9a). After adding ZnSO4, a negligible shift of the zeta 19 potential is observed in GF, indicating that there is no interaction between the Zn 2+ and GF powders, very different from the interaction between the Zn 2+ and CarraChi (Fig. R9b).

Updates in the Revised Manuscript:
We have added the zeta potential curves of GF powder in Supplementary Fig. 7 (Supplementary Information). We have also added a related discussion in the Revised Manuscript.
Line 136-139, Page 8: "After the addition of ZnSO4, the less negative zeta potential of −9.4 mV reveals the effective adsorption or crosslinking of Zn 2+ by the CarraChi, facilitating the desolvation of Zn 2+ during the deposition process, which differs from GF separator without adsorption toward Zn 2+ ( Supplementary Fig. 7).

The authors say a high transference number of Zn ions, and a fast desolvation process for Zn ions
in CarraChi gel-ZnSO4 can result in faster reaction kinetics of Zn metal electrodes compared to the GF case. It seems true since the Rct of Zn/Zn cell using CarraChi gel-ZnSO4 is lower than that of the cell using GF. However, the overpotential of the Zn/Zn cell using CarraChi gel-ZnSO4 is much higher than that of the cell using GF. Is this due to the low ionic conductivity of CarraChi gel-ZnSO4? Also, the authors claimed that using CarraChi gel-ZnSO4 can increase the CE of Zn/Cu cells. Due to some error points that show abnormal CEs for CarraChi gel-ZnSO4 cell, the average CE of cell using CarraChi 20 gel-ZnSO4 might be similar or a little higher than the cell of GF, but it seems like Zn/Cu cell using GF has higher CEs in most of the cycles before the 150th cycle. Please provide reasonable explanations for these circumstances.

Reply:
We thank the reviewer for the helpful comments. We wish to clarify below: Regarding "Is this due to the low ionic conductivity of CarraChi gel-ZnSO4?" We agree with the reviewer's point that the Zn/Zn cell using CarraChi shows a higher overpotential than that using a GF separator mainly because the ionic conductivity of CarraChi is low than the liquid electrolyte. ascribe lower Rct to suppressing corrosion reaction and higher overpotential to lower ionic conductivity.
We carried out more experiments to verify this explanation.
To reveal the effect of corrosion reaction on Rct, we carried out the EIS measurement for Zn|GF|Zn symmetric cells with different conditions, including fresh cells, after standing for 7 days, and after cycling (Fig. R10). A much higher Rct is obtained after standing for 7 days, demonstrating the occurrence of severe side reactions. The XRD patterns and SEM images further show that more byproducts formed in Zn|GF|Zn (Fig. R11). These results certify that the Rct is profoundly affected by the corrosion reactions.
Moreover, in comparison to the Rct after standing for 7 days, a much smaller Rct for Zn|GF|Zn symmetric cells is obtained after cycling, indicating the suppression of corrosion reactions during electrochemical cycling. Therefore, we believe that the overpotential is mainly determined by the ionic conductivity in the symmetric cell. Regarding "Zn/Cu cell using GF has higher CEs in most of the cycles before the 150th cycle" Although it seems like Zn/Cu cell using GF has higher CEs in most of the cycles before the 150th cycle, a much higher initial CE is achieved for CarraChi (92.7%) in comparison to GF (83.8%).
Therefore, the Zn|CarraChi|Cu exhibits a comparable average CE with Zn|GF|Cu before the 150th cycle. We have conducted more tests for the CE of a Zn/Cu cell using CarraChi, which is as high as 99.8% after 300 cycles (Fig. R12). The curves have also been updated in the Revised Manuscript.

Updates in the Revised Manuscript:
We have added the XRD patterns and SEM images of Zn foil soaked with CarraChi gel electrolyte and ZnSO4 in the revised Supplementary Information (Supplementary Fig. 12). We have updated the CE curves and data in Fig. 4d in the Revised Manuscript.
Line 207-209, Page 12: "Moreover, in comparison to the unstable Zn plating/striping less than 200 cycles with GF separator, the Zn anode with CarraChi gel electrolyte displays a stable CE for 600 cycles at 5 mA cm −2 , which is as high as 99.8% after 300 cycles ( Fig. 4d and 4e)." Line 156-160, Page 9: "The CarraChi gel electrolyte also reduces corrosion reactions between the Zn foil and ZnSO4, which is proved by the weaker peak intensity of by-products in the X-ray diffraction (XRD) patterns and the smooth surface in the SEM images in the anti-corrosion experiment compared to the Zn anode with liquid electrolyte and GF separator ( Supplementary Fig. 12)."

8.
Please provide the current density condition used for comparing the SEM image in Fig. 3f, and Supplementary Fig. 9a, b).

Reply:
We thank the reviewer for the helpful suggestion. The applied current density in Fig. 3f and Supplementary Fig. 14a, b is 10 mA cm -2 .
Updates in the Revised Manuscript: 23 We have updated the applied current density in the Revised Manuscript and Supplementary Information.

9.
Why is the rate capability of the full cell using CarraChi gel-ZnSO4 better than the reference case?
I believe using CarraChi gel-ZnSO4 can impinge the overpotential as is proved in Zn/Zn cell test.
Please also provide the voltage profile of the Zn|GF|ZVO and compare it in Fig. 5a.

Reply:
We thank the reviewer for the helpful comments. We wish to clarify below.
Regarding "the better rate performance of Zn|CarraChi|ZVO" It is true that a higher overpotential is observed for Zn|CarraChi|Zn. However, the transport kinetics of Zn 2+ should also be considered when assembling with the ZVO cathode. The higher tZn of the CarraChi gel electrolyte ensures an effective Zn 2+ supplement during the high-rate charge/discharge process. To reveal the transport kinetics of Zn 2+ , we carried out the EIS measurements for the full cells before and after cycling (Fig. R13). A smaller Rct is obtained for Zn|CarraChi|ZVO, demonstrating the improved redox kinetics and stable interface charge transfer even under high currents.
In addition to the decreased kinetics, dissolution of the ZVO cathode in 2M ZnSO4 (pH=4.3) may also contribute to the lower rate of Zn|GF|ZVO during the cycling, which can be evidenced by the yellow dissolved ZVO on the GF separator (Fig. R14). Regarding "comparing the voltage profile of the Zn|GF|ZVO" The voltage profile of the Zn|GF|ZVO is now provided in Fig. R15. The Zn|CarraChi|ZVO cell shows a higher overpotential than that of the Zn|GF|ZVO cell at 0.2 A g -1 , but much lower overpotential than 25 the Zn|GF|ZVO cell from 0.5 to 4 A g −1 , demonstrating the improved redox kinetics of Zn|CarraChi|ZVO under higher current density (Fig. R15).

Updates in the Revised Manuscript:
We have provided the voltage profiles of Zn|GF|ZVO in Supplementary Fig. 18 in the Revised Supplementary Information. We have also provided the optical images of CarraChi and GF after standing with ZVO cathode in Supplementary Fig. 19.
Line 249-250, Page 15: "The superior cycling stability due to effective suppression of dendrite and ZVO dissolution ensures the long life of the Zn batteries ( Supplementary Fig. 19)."

10.
Lastly, please compare the refillable pouch cell test result in Fig. 4g and Fig. 5f with the GF cells.

Reply:
We thank the reviewer for the helpful suggestion. We first tested the refillable pouch cell with a GF separator. For the Zn|GF|Zn pouch symmetric cell, the short circuit occurs when the capacity increases to 2 mAh cm -2 at 10 mA cm -2 in the pouch cell (Fig. R16a), which is due to the dendrite piercing into the porous GF, proved by the EIS curves (Fig. R16b). This is in sharp contrast to the stable cycling of Zn|CarraChi|Zn pouch symmetric cell with 35 mAh cm -2 . 26 Fig. R16. a, Cycling performance of the symmetric Zn|GF|Zn pouch cell with various capacities from 1 to 10 mAh cm -2 at 10 mA cm -2 . b, EIS curve of the Zn|GF|Zn pouch cell after cycling.
We also tested the cycling stability of Zn|GF|ZVO battery in a pouch cell as a control. A short circuit occurred after cycling for 23 cycles, which is also verified by the abnormal voltage curves and EIS result ( Fig. R17 and Fig. R18). These results confirm the infeasibility of using the GF separator for large-format cells.

Updates in the Revised Manuscript:
We have provided the cycling performance of the symmetric Zn|GF|Zn pouch cell in Supplementary   Fig. 16. We have also added the cycling performance of the Zn|GF|ZVO pouch cell in Fig. 5f in the Revised Manuscript. The voltage profile and EIS curves of the Zn|GF|ZVO pouch cell was also added in Supplementary Information (Supplementary Fig. 22). Related discussion has been added in the Revised Manuscript. has an initial capacity of 0.9 Ah and excellent cycling stability, retaining 84% capacity after 200 cycles, superior to full cells using liquid electrolytes and GF separator ( Fig. 5f and Supplementary Fig. 22).
This performance is also much better than that of the previously reported pouch full cells (Supplementary Table 7)." 28 Reviewer #3: The present manuscript proposed a hydrogel that can be prepared on a large scale and a refillable battery design. Indeed, the overall electrochemical performance of the ZIBs has been improved in this study. However, the work fails to reflect the big progress in the development of highperformance ZIBs. Many studies proposed hydrogel systems. The current work just selected a different raw material that has been commercialized. The proposed battery design also disables addressing the key challenge of ZIBs, such as HER and long-cycling stability of the cathode. In all, the proposed concept of the scalable synthesis of hydrogel and battery design cannot present an impressive innovation. Thus, I do not support the acceptance of the manuscript for publication in the present form.

Reply:
We thank the reviewer for the positive comment that "the overall electrochemical performance of the ZIBs has been improved in this study". We respectfully disagree that "the work fails to reflect the big progress in the development of high-performance ZIBs" and "just selected a different raw material". This work mainly presents a new battery design, namely the refillable and largeformat configuration, for large-scale aqueous batteries with a great leap of performance forward, whereas the employed hydrogel material or its synthesis is not the core point. We have to say sorry for not having explained the innovation point of this work very well in our previous version. We wish to clarify herein: Regarding "the work fails to reflect the big progress in the development of high-performance ZIBs." The core point of the submitted work is the refillable and large-format configuration for the aqueous batteries which is enabled by the designed CarraChi gel electrolyte. This configuration aims to address issues including gas build-up, battery swelling, and electrolyte consumption in practical large-scale batteries.
With this cell design, Zn metal anodes have a greatly improved performance, realizing an areal capacity of 35 mAh cm −2 (DOD of 65%) and a record-high cumulative cycling capacity of 1286 Ah at 10 mA cm −2 in pouch cells, 100 times higher than the capacities of state-of-the-art Zn cells in the literature (generally < 10 Ah, Fig. 4h). For Zn-ion full batteries, we have compared the electrochemical performance of the Zn|CarraChi|ZVO with previously reported pouch cells in Table R3 (Supplementary Table 7 in Supplementary Information). Our ZIB shows a much-improved capacity 29 and cycling life. We believe these results reflect the great progress in high-performance aqueous Zn batteries.

Regarding "The current work just selected a different raw material that has been commercialized."
We note that the core innovation of this work is the refillable and large-format configuration for large-scale aqueous batteries. The use of the CarraChi gel is a means to realize our design of the refillable and large-format battery configuration and address issues therein, including electrolyte leakage, fast water evaporation, lamination, and assembly of large pouch cells.
Therefore, this work does not intend to report a gel electrolyte. It is because of the new battery configuration enabled by the CarraChi gel electrolyte that we achieve the aforementioned practicallyapplicable high areal capacity (35 mAh cm −2 ), current density, DOD (65%), cycle life (>4000 h), record-high cumulative capacity (1286 Ah at 10 mA cm −2 ), which are challenging to for Zn batteries using conventional liquid/gel electrolytes without this battery design.

Regarding "The proposed battery design also disables addressing the key challenge of ZIBs, such as HER and long-cycling stability of the cathode."
The core innovation of our work is the refillable and large-format configuration for the aqueous batteries. Such a unique configuration addresses the key challenges in large-scale batteries including gas build-up, battery swelling, and electrolyte consumption. Meanwhile, the use of the CarraChi gel electrolyte is beneficial to suppress the dendrite growth, HER, and water evaporation, ensuring a longterm lifespan.
Regarding HER, HER is not likely to be eliminated completely because HER is thermodynamically favorable on the Zn metal surface in an aqueous environment. As we discuss further below, our CarraChi gel electrolyte reduces HER; our open-system battery also enables releasing any generated gas in large-format cells. As a result, the long-cycling stability of the full cells is much improved in large-format pouch cells. We have compared the performance of Zn|CarraChi|ZVO pouch cells with previously reported ZIB pouch cells in Table R3. It is seen that the Zn|CarraChi|ZVO pouch cell with our proposed battery design exhibits superior cycling stability under high capacity.
This new design realized significant advances in the performance of ZIBs, especially overall capacity.
Such a refillable battery configuration may introduce a paradigm shift in understanding and designing aqueous batteries for large-scale energy storage. 31 In addition, we have carefully addressed all the reviewer's concerns in our point-by-point responses below. We have also revised our manuscript to better illustrate our idea and findings according to the reviewer's comments.

1.
The authors proposed a hydrogel enabling to suppress the electrolyte loss. However, why do the authors need to refill the water? Refilling water means that the electrolyte will be consumed or can not be preserved very well in this system. In this situation, there is an obvious contradiction between the proposed concept and experimental results. Meanwhile, the authors should clarify why the electrolyte is consumed or can not be preserved even though hydrogel has been used in this manuscript. Does the refilled water affect the electrolyte concentration and further the electrochemical performance? If it does, it represents that the as-proposed battery design may fail to maintain the electrochemical performance. If it doesn't, the authors need to elaborately explain why the electrochemical performance does not change even though the electrolyte concentration changes after refilling the water. Additionally, as claimed that the hydrogel can suppress HER, but why do the authors still need to design a gas outlet?
Reply: We thank the reviewer for the helpful comments. Here are the answers to each of these questions.

Regarding "why do the authors need to refill the water?" and "contradiction between the proposed concept and experimental results"
This work intends to build large-format aqueous ZIBs, which are challenged by gas build-up, battery swelling, and electrolyte consumption over long-term cycling. We propose the open system to effectively solve the issues of gas build-up and battery swelling. As water consumption is almost inevitable in large ZIBs over long-time cycling due to the thermodynamically favored HER, we solve the water consumption issue by refilling water.
Due to the capability of the CarraChi gel with abundant polar functional groups (-OH, -NH2, -SO4 2− ) to bond H2O molecules, we use the CarraChi gel to preserve water, prevent electrolyte leakage and reduce water consumption. However, water consumption is almost inevitable in large-format 32 ZIB cells over long-term cycling due to HER side reaction (even if it is greatly suppressed). We take

advantage of the open-system cell configuration to refill water into the cells, which is simple and
cost-effective, so as to supplement any consumed water to ensure good performance and long life (more than 4000 h in Fig. 4g).
Thus, using the proposed battery design and refilling water are not contradictory, but together contribute to high-performance, long-life, large-scale ZIBs.

Updates in the Revised Manuscript:
Line 65-67, Page 4: "The crosslinked k-carrageenan and chitosan (CarraChi) gel electrolyte has numerous polar functional groups (-OH, -NH2, -SO4 2− ) that bond water molecules to suppress fast electrolyte evaporation and the HER." Regarding "Does the refilled water affect the electrolyte concentration and further the electrochemical performance?" We aimed to design the refillable and large-format configuration for the large-format Zn batteries.

Suitable water refilling can be an effective method to sustain the electrolyte concentration (ionic conductivity) of the CarraChi gel electrolyte in large-format cells.
In this work, the water refilling ensures good ionic conductivity and electrochemical cycling performance, which is proved by the long cycle life and slightly decreased overpotential after refilling the water or electrolyte in Fig. 4g.
It should be noted that evaporation of the water can lead to the salting-out of some ZnSO4 in the CarraChi electrolyte, which is harmful to the Zn 2+ transport. Refilling water helps redissolve the ZnSO4 in the CarraChi, and maintains the proper concentration in the gel electrolyte. Moreover, considering the low cost of ZnSO4 (~8.2 USD kg −1 ), the ZnSO4 solution can also be used to supplement the electrolyte consumption once the polarization potential increases markedly (Fig. 4g).

Updates in the Revised Manuscript:
Line 214-219, Page 12: "The pouch cell has an ultralong life of ~4000 h (65% DOD) with an areal capacity of 35 mAh cm -2 at 10 mA cm -2 (Fig. 4g). When the overpotential increased markedly due to electrolyte consumption during cycling, pure water or 2 M ZnSO4 was refilled to sustain the ionic conductivity for normal operation, which is indicated in the voltage-time curves (Fig. 4g). The electrochemical impedance spectroscopy (EIS) curves before and after cycling also confirm that no short circuit occurred during cycling (Fig. 4h)." Regarding "as claimed that the hydrogel can suppress HER, but why do the authors still need to design a gas outlet?" In general, the HER cannot be completely eliminated because metallic Zn is thermodynamically unstable in aqueous environments. The HER inevitably occurs on the Zn-electrolyte interface in 2M ZnSO4 electrolyte (pH=4.3). In our work, the designed CarraChi gel can mitigate the HER by destructing the H-bond network between water molecules, which are responsible for fast proton transport. Therefore, the HER can be suppressed by the CarraChi gel electrolyte significantly.
However, we do not seek to completely eliminate HER in large-format ZIBs over long-term cycling (which we believe is unlikely). Instead, we design the open-system battery with the gas outlet to avoid H2 accumulation and battery swelling, thereby circumventing problems caused by HER, especially for large-scale, long-life batteries.
2. K-carrageenan and chitosan have been successfully commercialized for many years. Therefore, large-scale preparation of hydrogel using these two raw materials is not an innovation of this manuscript.

Reply:
We agree with the reviewer that the CarraChi gel can be prepared on a large scale. This is an advantage but not the main innovation of this work. The core point of this work is the refillable,

open-system battery configuration for large-scale aqueous batteries.
The use of the CarraChi gel in our work is a means to realize the open, refillable, large-format battery configuration. We used the CarraChi gel because it can prevent electrolyte leakage, reduce water evaporation, and also homogenize the electric field distribution for dendrite-free Zn deposition. 34 Moreover, the low cost and large-scale preparation of CarraChi ensure the production of practical large-format Zn batteries for large-scale energy storage.
As a result, our refillable cells with the CarraChi electrolyte achieve high capacity, current density, DOD, and ultralong lifespan, which are not possible for ZIB with GF separators or any other previously reported hydrogel electrolytes with traditional sealed cell configurations. It is our new battery design that enables large-format, practically applicable ZIBs. Figure 2h demonstrated that the tensile stress of Carrachi-ZnSO4 has evidently decreased compared with CarraChi, suggesting that some chemical bonds have changed in this gel because of Zn 2+ . Please make a detailed explanation of what happened to the gel when Zn 2+ was added. Authors should also supplement the visualization proof to demonstrate the gel can prevent dendrite penetration.

Reply:
We thank the reviewer for the suggested comments.

Regarding "Please make a detailed explanation of what happened to the gel when Zn 2+ was added."
The bonding effect occurs between the CarraChi gel and Zn 2+ after introducing Zn 2+ . It should be pointed out that the reduced tensile strength of the CarraChi-ZnSO4 than the dry CarraChi is due to the existence of H2O, as is evidenced by the tensile stress-strain curves of the dry and wet CarraChi gel (Fig. R19). To explain the bonding effect of CarraChi gel and Zn 2+ , we would better compare the CarraChi-ZnSO4 to CarraChi-H2O instead of dry CarraChi gel. The CarraChi-ZnSO4 has higher strainto-failure (45%) and tensile strength (14.2 MPa) than that of the CarraChi-H2O (12.1% and 12 MPa), which is ascribed to the cross-linking of Zn 2+ and the polar groups (-SO4 and -OH) in the hydrogel network. The bonding effect of CarraChi and Zn 2+ is also certified by the change of zeta potential in

Updates in the Revised Manuscript:
We have updated the stress-strain curve in Fig. 2h and added the following discussion in the Revised

Manuscript:
Line 110-112, Page 6: "Compared to the CarraChi-H2O, the mechanical strength increased after the Zn 2+ addition, possibly due to the bonding effect between divalent Zn 2+ and -SO4 2− /-OH functional groups in the hydrogel network. 40, 41 " Regarding "visualization proof to demonstrate the gel can prevent dendrite penetration" To visualize the prevention effect of the CarraChi membrane toward dendrite, we have carried out a deposition experiment using the symmetric cell at 10 mA cm −2 . A smooth Zn deposition is observed with the CarraChi gel electrolyte while the Zn dendrites are mixed with the GF separator, illustrating the effective suppression of Zn dendrites of the CarraChi membrane (Fig. R20). In contrast, the symmetric cell with the GF separator fails when the capacity increases to 20 mAh cm -2 , indicating the short circuit of the symmetric cell. The optical images after cycling in the full cell also reveal that the dendrite penetration occurs with the GF separator (Fig. R21).

Updates in the Revised Manuscript:
We have also added the following discussion in the Revised Manuscript: Line 177-179, Page 10: "In contrast, Zn is deposited in the holes of the GF separator with a capacity of 10 mAh cm -2 (Fig. 3h, i), followed by the short-circuiting of the symmetric cell when the capacity increases to 20 mAh cm -2 , certifying the separator piercing ( Supplementary Fig. 14c, d)." Thickness is not the major reason affecting the electrochemical performance. Particularly, the CarraChi has strong mechanical properties for preventing the Zn dendrite proliferation, good scalability for large-scale energy storage, and water-bonding properties to prevent water leakage in the open-system, large-format batteries. In contrast, the GF has poor mechanical strength and large-pore structure, easily producing Zn dendrites.

Updates in the Revised Manuscript:
We have also added the GF information in the Revised Manuscript: Line 338, Page 20: "The pouch symmetric cell was assembled with two identical polished Zn foils (8 × 8 cm 2 ), CarraChi gel, or a GF (type A, Whatman) was used as the separator."

Could the author describe what kind of barrier the gel layer provides for Zn surface diffusion?
Reply: We thank the reviewer for the helpful comments. According to previous reports (Energy Environ. Sci. 2019, 12, 1938-1949Adv. Mater. 2022, 34, 2202382), the interfacial energy barrier is provided with the gel layer. In our work, the changed zeta potential after ZnSO4 addition (Fig. 3a in the Revised Manuscript) reveals the effective adsorption of Zn 2+ by the CarraChi gel, which provides an additional energy barrier for absorbed Zn 2+ ions to move laterally, as also stated by the reduced 2D diffusion current (Fig. 3c). Therefore, these Zn 2+ ions are forced to deposit near the sites where the initial adsorption occurred, instead of the fewer sites with low surface energy.

Updates in the Revised Manuscript:
We have also added a related discussion about the deposition barrier in the Revised Manuscript: 6. It will be nice if the author could perform some simulations to visualize the electric field at the electrolyte-electrode interface that has been homogenized when gel electrolyte is used in this study.

Reply:
We thank the reviewer for the helpful suggestion. Following the suggestion, we carried out finite simulations to visualize the electric field and Zn 2+ concentration distribution at the electrolyteelectrode interfaces. As shown in Fig. R22, the Zn anode with CarraChi exhibits homogenized Zn 2+ concentration and electric field distribution along X-axis, which facilitates uniform Zn 2+ supplement 39 during the Zn deposition process. In contrast, a higher concentration gradient and nonuniform electric field are observed along X-axis for the Zn anode with GF separator, making it easier for Zn dendrites growth at the Zn/GF interface.

Updates in the Revised Manuscript:
We have provided the Zn 2+ concentration distribution of Zn|CarraChi|Zn and Zn|GFA|Zn symmetric cells in Fig. 3d and Fig. 3e, respectively, and the electric potential and electric current distribution in 7. "1.26V vs RHE at 5 mA cm -2 (S Fig. 12)" Please change Fig. 12 to Fig. 10. In Fig. 10, it indeed verifies HER can not be fully suppressed even using CarraChi gel because the onset potential for HER is almost the same, in which both start around -1.1 V. The difference is that the gel system shows a smaller current density compared with GF. In this case, it is incorrect to claim Fig. 10 demonstrates slower evolution kinetics. Importantly, please use ZnSO4 electrolyte rather than Na2SO4 electrolyte to test LSV.

Reply:
We thank the reviewer for pointing out this error. We have corrected the figure number and double-checked all figure numbers.
Regarding "it indeed verifies HER can not be fully suppressed even using CarraChi gel because the onset potential for HER is almost the same" In the Revised Manuscript, we compared the onset potential instead of the previously selected current density of the LSV. Since the onset overpotential is the applied potential with apparent cathodic currents, we carried out the iR correction for the LSV curves and calculated the onset overpotential 41 according to previous reports (Nat. Commun. 2019, 10:1348; Sci. Adv. 2015, 1, e1500259). The onset potential is the point where the oblique line extension intersects the line parallel to the horizontal axis.
The battery with the CarraChi exhibits a more negative onset potential of -1.40 V, in comparison to that with the GF separator (-1.26 V), illustrating the effective suppression of HER by CarraChi (Fig.   R23).
In addition, as we explained above, the HER in ZIBs is not likely to be completely eliminated because

Updates in the Revised Manuscript:
We have corrected HER curves in the revised Supplementary Information (Supplementary Fig. 10).
We have also added the following discussion in the Revised Manuscript: Line 152-154, Page 9: "The suppressed HER on the Zn anode with CarraChi is also proved by a much lower onset overpotential (−1.40 V vs. standard hydrogen electrode, SHE) than that with a GF separator (−1.26 V vs. SHE) (Supplementary Fig. 10)." 8.  R24). However, very few papers reported average CE by this method. To fairly compare the CE with previous reports, we have chosen the more widely-used testing method and used the CE data after stabilizing.
9. It should be more subjective when the authors conclude. The good capacity retention of Zn|CarraChi|ZVO is not only related to the effective suppression of Zn dendrite growth but also the inhibition of self-corrosion and side reactions of Zn foil.

Reply:
We thank the reviewer for the helpful comments. We agree that although good capacity retention is mainly ascribed to the prevention of the Zn dendrites, the inhibition of self-corrosion and side reactions also plays an important role in determining good cycling stability.
Following the reviewer's suggestion, we carried out a soaking experiment by leaving the assembled symmetric cells with or without CarraChi for 1 week to research the degree of Zn corrosion. The experimental results show that the Zn in the Zn|CarraChi|Zn cell has a much weaker peak intensity of by-products in the XRD patterns (Fig. R25a). SEM images also reveal that a smooth surface of the Zn foil can be observed with CarraChi (Fig. R25b). In contrast, a Zn foil soaked in 2M ZnSO4 solution is covered with dendritic by-products of zinc hydroxide sulfate (Fig. R25c). Therefore, the CarraChi gel has a positive effect on mitigating the zinc hydroxide sulfate byproducts.
In all, the good capacity retention of Zn|CarraChi|ZVO is ascribed to the effective suppression of Zn dendrite growth, the inhibition of self-corrosion and side reactions of Zn foil

Updates in the Revised Manuscript:
We have added the XRD patterns and SEM images of Zn foil soaked with CarraChi gel electrolyte and ZnSO4 in the revised Supplementary Information (Supplementary Fig. 12). We have also added the following discussion in the Revised Manuscript: Line 156-160, Page 9: "The CarraChi gel electrolyte also reduces corrosion reactions between the Zn foil and ZnSO4, which is proved by the weaker peak intensity of by-products in the X-ray diffraction 10. the author should explain why ZVO in GF almost shows the same specific capacity as CarraChi before 40 cycles in Figure 5c, while the specific capacity of GF is higher or lower than CarraChi in Figure 5b. Please mention which current density has been used in Figure 5f.

Reply:
We thank the reviewer for the valuable comments. In Fig. 5b, we show that the full cell with CarraChi has a better rate performance than that with GF. The fluctuating capacity of GF-based batteries may be due to unsatisfying battery assembling or unstable performance using the GF separator. We have conducted more tests of the rate performance of Zn|GF|ZVO (Fig. R26). In particular, a significant capacity decay can be observed for Zn|GF|ZVO, which can be ascribed to the fast dissolution of ZVO in the 2M ZnSO4.
In Fig. 5c, the reason why both cells show the same capacity retention ratio before 30 cycles are that the application of the CarraChi gel electrolyte will not affect the initial capacity. However, CarraChi suppresses the dissolution of the ZVO cathode into the electrolyte during long cycling. We found a 45 yellow substance adsorbed on the GF separator which is ascribed to the dissolved ZVO (Fig. R27). In contrast, there is no dissolved ZVO on the CarraChi gel. The dissolution of the ZVO cathode into the liquid electrolyte with GF caused significant capacity decay with GF after 30 cycles.  In addition, in Fig. 5f, the applied current density is 0.2 A g −1 . We have added the testing condition in Fig. 5f.
Updates in the Revised Manuscript: 46 We have updated the rate performance of Zn|GF|ZVO in Fig. 5b and the applied current density 0.2 A g −1 in Fig. 5f in the Revised Manuscript.

Reviewer #1:
The revised version is much improved. The authors adequately respond to the comments raised by the reviewers. The revised version is acceptable for publication.

Reply:
We thank the reviewer for the positive comments and recommendation for publication in Nature Communications.
Reviewer #2: I think further revision is required because there are some unclear statements in the authors' rebuttal letter.

Reply:
We sincerely thank the reviewer for providing constructive comments in the two-round reviewing processes, which have improved our work to be more rigorous.
To ensure clearer expression, we have supplemented relevant discussions and explanations. Please see our point-by-point responses below.
1. Considering that the concentration of proton is very low in mild acidic electrolyte conditions (pH above 4.5), I believe the direct reduction of water is the main problem of HER. Direct water reduction can be accelerated by inducing a stronger interaction between water molecules and other solvents or ions than the interaction between the water molecules. This is because, with a stronger interaction, water tends to undergo stronger polarization.  Fig. 12 and Supplementary Fig. 10), which is different from the slow passivation of Zn foil in pure water, which may indicate that the H + reduction in 2M ZnSO4 electrolyte is the main cause of HER. Notably, this research primarily emphasizes an application-oriented Zn battery, and we anticipate future collaborations with fellow researchers to undertake in-depth investigations into fundamental aspects of HER.
We agree with the reviewer that water molecules bonding with CarraChi should also be strongly polarized, resulting in a higher degree of direct water reduction. However, the solvated H2O near the Zn metal is also responsible for the HER during the electrochemical process (Nature, 2021, 600, 81-85; Adv. Mater. 2022, 2206754). The CarraChi can not only bond with free water but also modulate the solvation structures of Zn 2+ , which is certified by the Raman results and zeta potential ( Fig. 3a and Supplementary Fig. 9). Thus, the bonding between CarraChi and water molecules does not aggravate the HER. Instead, as the H-bonding network is disrupted by CarraChi, HER is suppressed, as demonstrated by the much lower overpotential ( Supplementary   Fig. 10).
Regarding the challenge of cathodes, as our open-system battery enables releasing any generated gas in large-format cells, we achieved full cells with much-improved cycling stability in large-format pouch cells. We have compared the performance of Zn|CarraChi|ZVO pouch cells with previously reported ZIB pouch cells in Supplementary Table 7. The Zn|CarraChi|ZVO pouch cell with our proposed battery design exhibits superior cycling stability with high capacity. Figure R5 should be provided again without IR correction. The effect of IR is obviously included in real cell operation.

Reply:
We thank the reviewer for the helpful comments. Following the reviewer's comments, we have updated the LSV curves without IR correction in the revised Supplementary Information (Supplementary Fig. 10). The onset potentials of the LSV curves are only slightly different with or without IR correction (Fig. R1). In addition, the Zn with CarraChi shows more negative HER onset potential than that with GF, suggesting that the CarraChi can suppress HER.

Updates in the Revised Manuscript:
We have updated the LSV curves in Supplementary Fig. 10 in the Revised Supplementary Information.
3. I believe the report from Archer's group suggests that the electrolyte's shear modulus is meaningless when the electrolyte has a sufficiently small pore structure. I believe this is not the case for the CarraChi electrolyte.

Reply:
We thank the reviewer for the instructive comments. According to Archer's study (J. Am. Chem. Soc. 2014, 136, 7395-7402), mechanical strength is not the only factor that affects dendrites. Small pore structures can also induce dendrite deposition along the pore, causing short-circuiting. We agree with the reviewer that this conclusion may not be applicable to our gel electrolyte. Based on the Reviewer's comments and literature study, we do not claim the inhibiting effect of mechanical strength on Zn dendrite growth. Still, the gel electrolyte with abundant oxygen-containing groups can induce uniform Zn nucleation and deposition, enabling dendrite-free plating/stripping, which is verified by the SEM images after cycling with the CarraChi gel electrolyte (Fig. 4c).
In the Revised Manuscript, we have revised the discussion on mechanical strength, no longer stating the controversial dendrite-inhibiting capability of mechanical strength.

Updates in the Revised Manuscript:
Line 112-114, Page 6: "Such an improved mechanical property of the CarraChi gel electrolyte is expected to facilitate the electrode fabrication and battery assembling process. 42 " 4. About the CE, it is questionable how the GF cell can have higher CE at certain cycles even though the GF cell suffers from a more severe HER problem than the CarraChi cell.

Reply:
We thank the reviewer for the useful comments. As the GF cells suffer from a more severe HER problem, the cycling performance and CE in the Zn|GF|Cu cells fluctuate significantly from different cells. Therefore, we have retested the CE of more Zn|GF|Cu cells. As shown in Fig. R2, the Zn|CarraChi|Cu cell (Fig. R2a) exhibits higher initial CE, higher average CE, and cycling stability than the Zn|GF|Cu cells ( Fig. R2bf) during the plating/stripping process.
Regarding the CE of the Zn|GF|Cu cells at specific cycles, we do find the CE in certain cycles of some Zn|GF|Cu cells is higher than that of the Zn|CarraChi|Cu cell, mainly found in around 10 cycles. We speculate that this is because of the relatively low initial CE of Zn|GF|Cu cells, leaving unreacted Zn metal on the Cu current collector, which gradually reacted in subsequent cycles, causing relatively high CE at ~10 th cycle in Zn|GF|Cu cells. Nevertheless, the average CE of the Zn|CarraChi|Cu cell is still better than that of Zn|GF|Cu.

Updates in the Revised Manuscript:
We have updated the CE curves and data in Fig. 4d in the Revised Manuscript. 5. In Zn/Zn symmetric cell, the overpotential for the CarraChi cell is much higher than the GF cell. However, the rate capability of the full cell using CarraChi seems to be better than the GF cell. To make this reasonable, the authors need to show that the CarraChi can decrease the overpotential of the positive electrode reaction. If the high transport kinetics of Zn 2+ is a really important factor, then why it does not affect the Zn/Zn symmetric cell performance?
Reply: We thank the reviewer for the helpful comments and suggestions. Indeed, as shown in Fig. R3, the Zn|CarraChi|ZVO cell shows a much lower overpotential than the Zn|GF|ZVO cell from 0.5 to 4 A g −1 .
In symmetric cells, the electrolyte/separator determines the ion conductivity and overpotential. In full cells, the cathode largely determines the reaction kinetics due to the complicated Zn 2+ intercalation/deintercalation mechanisms in the full cells. We thus deduce that in full cells, the transport kinetics of Zn 2+ in the cathode has a more significant effect on the rate performance than the overpotential caused by the electrolyte/separator.
Thus, as the overpotential in the positive electrode is decreased in the CarraChi cells ( Fig. R3), it is reasonable that the rate capability of the full cells using CarraChi is better than the GF cells.